The present invention relates in general to a system and method for detecting, quantizing and classifying particle fallout contamination.
Many facilities, such as clean rooms, require monitoring of particle fallout contamination to insure that the facilities maintain a desired cleanliness level. One known cleanliness monitoring technique used by the aerospace industry employs a gridded witness filter which is placed in the clean work area so that fallout particles will be deposited thereon. After a predetermined time interval, the filter is taken to a laboratory where the particles are manually counted, sized and classified. This technique has a number of disadvantages. First, handling of the witness filter can easily change the sample prior to analysis through disruption of the deposited particles, or collection of additional particles not attributable to the work area. Second, the measurement is in no way real-time, and thus cannot provide any indication of severe contamination, for example, as it occurs. Finally, the need for manually counting the collected particles requires a large amount of labor and is highly susceptible to human errors.
Instruments also exist which are based on side-scattered light measurement or on particles falling through a laser grid and interrupting the laser beam, thereby producing a pulse of light which is counted. Although these instruments eliminate the need for manual particle counting, the instruments do not actually image the particles, and at best produce only an estimate of the number of particles and their sizes.
A need therefore exists for a particle surface contamination detector which can automatically provide analysis of fallout particle numbers and sizes, as well as real-time measurements of particle fallout rates.